A variety of techniques and instruments have been developed for use in the removal or repair of tissue in arteries and similar body passageways. A frequent objective of such techniques and instruments is the removal of atherosclerotic plaques in a patient's arteries. Atherosclerosis is characterized by a build-up of fatty deposits (atheromas) in the intimal layer (under the endothelium) of a patient's blood vessels. Very often over time, what Is initially deposited as relatively soft cholesterol-rich atheromatous material hardens into a calcified atherosclerotic plaque. Such atheromas restrict the flow of blood, and therefore often are referred to as stenotic lesions or stenoses, the blocking material being referred to as stenotic material. If left untreated, such stenoses can cause angina, hypertension, myocardial infarction, strokes and the like.
Several kinds of atherectomy devices have been developed for attempting to remove some or all of such stenotic material. In one type of device, such as that shown in U.S. Pat. No. 4,990,134 (issued to Auth), a rotating burr covered with an abrasive cutting material such as diamond grit (diamond particles or dust) is carried at the distal end of a flexible drive shaft. One atherectomy device commercially available from Heart Technologies, Inc. of Bellevue, Washington, U.S.A. is sold under the trade name Rotablator. The design of the Rotablator device is, to a significant extent, based on the design described in the Auth patent and the Rotablator device is typically rotated at speeds in the range of about 150,000-190,000 rpm.
Auth's burr is made from a solid, inflexible metal which is physically attached to a flexible, trifilar, helically wound drive shaft. This solid burr must be kept relatively short in order to allow the burr to navigate the bends and curves in tortuous arteries. At the same time, it must be sufficiently long to ensure reliable fixation of the burr to the drive shaft.
Another type of atherectomy device is shown in U.S. Pat. No. 5,314,438 (issued to Shturman). This design provides a solution for the problems associated with fixation of a separate burr to a drive shaft by eliminating the burr altogether. The abrasive drive shaft atherectomy device disclosed in the above-mentioned Shturman patent typically is used over a guide wire and includes a flexible, elongated drive shaft made from one or more helically wound wires. Wire turns of the proximal segment of the drive shaft have a generally constant diameter, while wire turns of a segment of the drive shaft near its distal end have an enlarged diameter. At least part of the enlarged diameter segment includes an external coating of an abrasive material to define an abrasive segment of the drive shaft which, when rotated at high speeds, is usable to remove stenotic tissue from an artery.
Manufacturing some of the embodiments of the device shown in the above-mentioned Shturman patent can be relatively time-consuming. This is particularly true with respect to the embodiments of the device which use two helically wound layers, such as the one shown in FIG. 8 of that reference. In that drawing and some of the other embodiments depicted in the Shturman patent, wire turns of the enlarged diameter segment of the drive shaft are supported by a bushing. Even though this bushing may be made of a flexible material, it does decrease somewhat the flexibility of the enlarged diameter abrasive segment of the drive shaft. Unless a bushing within the enlarged diameter segment is used, though, adjacent wire turns of this segment can fall out of alignment with one another when the enlarged diameter segment of the drive shaft is bent around a curve.